Oil wells typically vary from a depth of a few hundred feet to several thousands and in many instances can exceed 10,000 feet in depth. In many oil wells there is insufficient in situ pressure to affect the flow of oil out of the well to the surface. For that reason a variety of different pumping and extraction devices have been developed to pump or urge oil from a well. The most common of such devices is a reciprocating pump that is installed deep within the well and operated by a reciprocating pump or sucker rod extending from the pump to the well head at the ground surface.
A significant amount of effort has been directed toward the development of various devices that can be utilized in order to reciprocate a pump or sucker rod in an effective manner to extract oil from a well. Traditionally the pump rod has been reciprocated by a device known as a pump jack which operates through the rotation of an eccentric crank driven by an electric, gasoline or diesel motor. Such mechanical drive mechanisms have been utilized extensively in the oil production industry for decades and continue to be the primary method for extracting oil from a well. However, they suffer from a number of inherent disadvantages or inefficiencies. These inefficiencies include their substantial size and weight that makes them expensive to produce, difficult to transport and expensive to install. The mass of such units also requires significant structural support elements at the well head which adds to the complexity and expense of the overall drive system. Furthermore, mechanical drive systems have components that are physically linked or connected in some form by way of connecting rods, cams, and gear boxes. For a variety of different reasons it often becomes necessary to adjust the travel of the pump rod. Mechanical linkages, as have previously been used, present difficulties in adjusting the travel or displacement of the pump rod. Under prior art devices adjusting rod displacement and pumping speed requires the drive system to be shut down, wasting valuable production time and increasing labour costs. Mechanically driven pump jacks are also limited in their ability to control acceleration and deceleration of the pump rod during its reciprocation.
To combat these limitations in mechanical pump jack drive systems, others have proposed a variety of different pneumatic and hydraulic drive mechanisms that have met with varying degrees of success. Most require the placement of some form of hydraulic cylinder on the well head to raise and lower the pump rod. Such drive systems utilize a connecting rod that is driven, through an eccentric cam or crank, by an electric, gasoline or diesel motor. Since the primary mode of powering the drive systems remains a mechanical linkage, such systems, to a large extent, still suffer from the same inherent difficulties of rod speed and stroke control as do the prior purely mechanical pump jacks.